1 Field of the Invention
The present invention relates to software controlled radios and, more particularly, to Global Positioning System-based digital compensation of radio frequencies used in software controlled radios.
2. Description of the Related Art
The use of software controlled radios has increased substantially in recent times. Software controlled radios are used in applications including wireless digital telephones, digital televisions, and numerous other forms of wireless digital data transfers. When generating and receiving radio signals, precise frequency control is needed to define communication channels and to stay within regulatory limits. The precise control of radio frequencies allows for a more efficient use of the radio spectrum by minimizing the amount of deadband needed between radio channels to accommodate frequency tolerances.
Conventional software controlled radio systems generally use high quality, temperature stabilized, crystal oscillators to control the radio frequencies used. In extreme cases, atomic clocks may be used to control these radio frequencies. These methods of radio frequency control generally are more expensive and consume more power than the use of simple crystal oscillators.
The Global Positioning System's (GPS) one-pulse-per-second (PPS) signal has been used to directly stabilize the frequency of an oscillator. While this system uses GPS to measure the frequency error, it uses analog techniques to alter the oscillator frequency and make the frequency precisely correct. Consequently, this system still generally requires the use of high cost oscillators to achieve precise frequency control.
Therefore, it would be desirable to have an apparatus and method for controlling the communication frequencies of a software controlled radio by using GPS signals to measure the inaccuracies of one or more local oscillators and then digitally compensating within the software controlled radio for the local oscillator inaccuracies.